linux内存管理的初始化

　　ENTRY(startup_32)

　　/*

　　* Set segments to known values.

　　*/

　　cld

　　lgdt boot_gdt_descr - __PAGE_OFFSET  /* 设置段寄存器 */

　　movl $(__BOOT_DS),%eax

　　movl %eax,%ds

　　movl %eax,%es

　　movl %eax,%fs

　　movl %eax,%gs

　　/*

　　* Clear BSS first so that there are no surprises...

　　* No need to cld as DF is already clear from cld above...

　　*/

　　xorl %eax,%eax

　　movl $__bss_start - __PAGE_OFFSET,%edi

　　movl $__bss_stop - __PAGE_OFFSET,%ecx

　　subl %edi,%ecx

　　shrl $2,%ecx

　　rep ; stosl

　　/*

　　* Copy bootup parameters out of the way.

　　* Note: %esi still has the pointer to the real-mode data.

　　* With the kexec as boot loader, parameter segment might be loaded beyond

　　* kernel image and might not even be addressable by early boot page tables.

　　* (kexec on panic case). Hence copy out the parameters before initializing

　　* page tables.

　　*/

　　movl $(boot_params - __PAGE_OFFSET),%edi

　　movl $(PARAM_SIZE/4),%ecx

　　cld

　　rep

　　movsl

　　movl boot_params - __PAGE_OFFSET + NEW_CL_POINTER,%esi

　　andl %esi,%esi

　　jnz 2f   # New command line protocol

　　cmpw $(OLD_CL_MAGIC),OLD_CL_MAGIC_ADDR

　　jne 1f

　　movzwl OLD_CL_OFFSET,%esi

　　addl $(OLD_CL_BASE_ADDR),%esi

　　2:

　　movl $(saved_command_line - __PAGE_OFFSET),%edi

　　movl $(COMMAND_LINE_SIZE/4),%ecx

　　rep

　　movsl

　　1:

　　/*

　　* Initialize page tables.  This creates a PDE and a set of page

　　* tables, which are located immediately beyond _end.  The variable

　　* init_pg_tables_end is set up to point to the first "safe" location.

　　* Mappings are created both at virtual address 0 (identity mapping)

　　* and PAGE_OFFSET for up to _end+sizeof(page tables)+INIT_MAP_BEYOND_END.

　　*

　　* Warning: don't use %esi or the stack in this code.  However, %esp

　　* can be used as a GPR if you really need it...

　　*/

　　page_pde_offset = (__PAGE_OFFSET >> 20);

　　movl $(pg0 - __PAGE_OFFSET), %edi

　　movl $(swapper_pg_dir - __PAGE_OFFSET), %edx

　　movl $0x007, %eax   /* 0x007 = PRESENT+RW+USER */

　　10:

　　leal 0x007(%edi),%ecx   /* Create PDE entry */

　　movl %ecx,(%edx)   /* Store identity PDE entry */

　　movl %ecx,page_pde_offset(%edx)  /* Store kernel PDE entry */

　　addl $4,%edx

　　movl $1024, %ecx

　　11:

　　stosl

　　addl $0x1000,%eax

　　loop 11b

　　/* End condition: we must map up to and including INIT_MAP_BEYOND_END */

　　/* bytes beyond the end of our own page tables; the +0x007 is the attribute bits */

　　leal (INIT_MAP_BEYOND_END+0x007)(%edi),%ebp

　　cmpl %ebp,%eax

　　jb 10b

　　movl %edi,(init_pg_tables_end - __PAGE_OFFSET)

　　#ifdef CONFIG_SMP

　　xorl %ebx,%ebx    /* This is the boot CPU (BSP) */

　　jmp 3f

　　/*

　　* Non-boot CPU entry point; entered from trampoline.S

　　* We can't lgdt here, because lgdt itself uses a data segment, but

　　* we know the trampoline has already loaded the boot_gdt_table GDT

　　* for us.

　　*/

　　ENTRY(startup_32_smp)

　　cld

　　movl $(__BOOT_DS),%eax

　　movl %eax,%ds

　　movl %eax,%es

　　movl %eax,%fs

　　movl %eax,%gs

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